1. Field of the Invention
The present invention relates to central tire inflation systems (CTIS), also known as onboard inflation systems and tire traction systems, wherein the inflation pressure of one or more vehicle tires may be controlled from a remote location (usually the vehicle cab) with the vehicle at rest and/or in motion and utilizing an onboard source of pressurized fluid (usually compressed air from the vehicle air brake compressor and/or a compressed air reservoir). In particular, the present invention relates to a valve assembly mountable at the tire rim, or within the tire rim, which is vented only through the single conduit connecting same to the system control valves, which is effective to open and close in response to fluid pressure in the single conduit and which is effective to automatically fluidly isolate a tire when the pressure to which the tire is inflated is less than a minimum reference pressure.
2. Description of the Prior Art
Central tire inflation systems, also known as tire traction systems, are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 2,634,782; 2,976,906; 2,989,999; 3,099,309; 3,102,573; 3,276,502; 3,276,503; 4,313,483; 4,418,737, 4,421,151 and 4,434,833, the disclosures of all of which are hereby incorporated by reference. CTIS allow the operator to remotely manually and/or automatically vary and/or maintain the inflation pressure of one or more of the vehicle tires from the vehicle (usually a truck) air system, usually while the vehicle is in motion as well as when the vehicle is at rest.
It is well known that the traction of vehicles on relatively soft terrain (i.e. on mud, sand or snow) may be greatly improved by decreasing the inflation pressure within the tires. By decreasing the inflation pressure, the tire supporting surface (usually called the "footprint") will increase thereby enlarging the contact area between the tires and the terrain. Additionally, it is often desireable to decrease the tire pressure from the over-the-road or highway inflation pressure to increase riding comfort on rough roads. On the other hand, higher tire pressures decrease rolling resistance and tire carcass temperatures on smooth roads thereby increasing economy and safety. Accordingly, in cross country vehicles it is desireable to change the inflation pressure in the pneumatic tires to fit the terrain and is also desireable that a system be provided for changing the inflation pressure of the tires from an onboard source, while the vehicle is at motion or at rest and that the system be controlled from the vehicles operating cab. This is especially true for military vehicles which usually travel in columns whereby stoppage of the vehicle would delay the entire column. Additionally, if the military is under enemy attack, it is imperative that the vehicle maintain its maneuverability as long as is possible. If a tire has been damaged by gun fire or the like, it is desireable to be able to at least partially inflate the damaged tire, if possible, so that the vehicle remains mobile.
While CTIS are known in the prior art and have been utilized by the U.S. Army since at least World War II, the prior art systems are not totally satisfactory as the systems utilize conduits, valves and/or seals which were located at exposed locations rendering same vulnerable to damage over rough terrain, utilize valves and/or conduits which required venting at the wheel hub location thus exposing same to malfunction as a result of clogging due to water, mud, snow or the like, do not provide for automatic isolation of a vehicle tire subject to extreme damage, subject the rotary seal members to a differential pressure during steady state operating conditions thereby decreasing the life thereof and increasing the likelihood of leakage, and/or require drilling of passages in the axle housing and/or hub assemblies which may tend to weaken same and/or render retrofit of a CTIS to an existing vehicle more difficult and costly.